Now, I was able to get some time to create a minimal Spring MVC web application and see how it performs on GAE. Below is the result. The web.xml loads the ContextLoaderListener and DispatcherServlet. The application context is empty (i.e. no beans). The dispatcher-servlet.xml contains a <context:component-scan /> tag and a ViewResolver. It takes about 6.75 seconds for a loading request (approximately cpu_ms=3600).

6.75 seconds for a loading request is probably not much. But the 1100 cpu_ms by slim3 is sure enviable. I also found this article helpful in explaining the cause of increase in loading request time.